Metal-coated abrasives, grinding wheel using metal-coated abrasives and method of producing metal-coated abrasives

ABSTRACT

The present invention provides an abrasive which can attain a sufficient retention force in a resinoid grinding wheel even in the case of a small grain size. The abrasive is produced by bonding plural abrasive grains coated with a metal layer by a metal. The metal layer is made of the metal selected from the group consisting of nickel, nickel-phosphorus, cobalt, cobalt-phosphorus, titanium, copper, chromium, iron, zirconium, niobium, molybdenum and tantalum. Also the abrasive grains are made of at least one selected from the group consisting of hard substances such as cubic boron nitride, diamond, alumina and silicon carbide, each having an average grain size within a range from 0.5 to 300 μm.

CROSS-REFERENCE TO RELATED APPLICATIONS.

This application is an application filed under 35 U.S.C. §111(a)claiming benefit pursuant to 35 U.S.C. §119(e)(1) of the filing date ofProvisional Application No. 60/372,431 filed on Apr. 16, 2002, pursuantto 35 U.S.C. §111(b).

TECHNICAL FIELD

The present invention relates to an abrasive used in grinding wheels,coated abrasives, or the like and, more particularly, relates to ametal-coated abrasive wherein the surface of abrasive grains is coatedwith metal to enhance a retention force by which the abrasive isretained.

BACKGROUND ART

A resinoid grinding wheel using a resin as a bonding material hasproblems in that abrasive often falls off during grinding, and thegrinding ratio of the grinding wheel is reduced because it has a lowretention force by which the abrasive is retained in a bond layer ascompared with a grinding wheel using other types of bond. Therefore,various proposals to increase the retention force by which the abrasiveis retained have been made.

Taking the case of a cubic boron nitride, there has been developed anabrasive whose surface is provided with single- or multi-layeredcoatings of nickel, nickel-phosphorus, cobalt, cobalt-phosphorus ortitanium, thereby improving retention force in a bond layer by means ofirregularity of the coated surface (see, for example, the followingPatent Applications), and the resulting abrasive is used in resinoidgrinding wheells at present.

Japanese Patent Application, First Publication No. Sho 60-51678.

Japanese Patent Application, First Publication No. Sho 59-142066.

Japanese Patent Application, First Publication No. Sho 59-30671.

Japanese Patent Application, First Publication No. Sho 60-52594.

Japanese Patent Application, First Publication No. Hei 9-323046.

For example, Japanese Patent Application, First Publication No. Sho60-51678 discloses a method of producing a nickel-coated abrasive, whichhas irregularities on the surface and also has a high retention force,by providing a metal layer on the surface of abrasive grains and alsoproviding a first layer made of a spongy nickel and a second layer madeof a dense nickel.

Also Japanese Patent Application, First Publication No. Sho 59-142066discloses a resinoid grinding wheel whose grinding ratio was improved byproviding a first layer made of nickel, a second layer made of cobalt,and a third layer made of nickel coating.

As described above, the retention force by which the abrasive isretained in the bond can be increased by coating the surface of abrasivegrains and, therefore, falling-off of the abrasive during grinding isreduced and the grinding ratio of the grinding wheel is improved.

However, the retention force between the metal-coated abrasive and theresinoid bond obtained by metal coating is a physical retention forcecaused by irregularities of the coated surface. As the grain size of theabrasive to be used decreases, small irregularities are formed on thecoated surface, and also the number of irregularities on the surface isreduced. Therefore, the contact area between the coated surface and thebond layer decreases, and the retention force by which the abrasive isretained in the resinoid bond becomes insufficient.

In the grinding process, the grain size of the abrasive must be reducedto improve the surface roughness of a work material. In the trend ofsize reduction and higher accuracy of workpieces, it has been stronglydesired by the industrial world to develop an abrasive having a smallgrain size even when used in a resinoid grinding wheel. However, asdescribed above, an abrasive having a very small grain size still has aproblem in that sufficient retention force is not attained even by metalcoating, and also has problems, for example, of increased tool cost dueto low grinding ratio, increase in total working cost due to increase inthe number of trueing and dressing operations for adjustment of grindingwheel size and restoration of cutting edge, and impairment of surfaceroughness of a work material due to falling-off of abrasive grains.Therefore, strong demand for improvement of the retention force by whichthe abrasive is retained in the resinoid bond still remained.

Japanese Patent Application, First Publication No. Hei 10-337670discloses a method of preventing early falling-off of abrasive withoutusing a metal coating, which comprises forming an abrasive (compositeabrasive grains) comprising abrasive grains bonded by a vitrified-bondmaterial or a metal bond material, thereby improving the retention forcein the resinoid bond by means of the irregularity portion.

Irregularity formed by bonding these abrasive grains improves theretention force by which the abrasive is retained in the resinoid bondand also improves the grinding ratio. However, composite abrasive grainsobtained by bonding abrasive grains using a vitrified-bond material or ametal bond material had problems in that strong bonding of the abrasivegrains give composite abrasive grains in the same state as in the caseof using abrasive grains having a larger grain size than that ofabrasive grains constituting the composite abrasive grains, and thus thevalue of the grinding power increases.

In a resinoid grinding wheel, when the value of the grinding powerincreases, phenomena such as deterioration of the resinoid bond andgrinding burn of a work material due to grinding heat are likely tooccur. To prevent these phenomena, it is important to maintain lowvalues of grinding power (to maintain the sharpness).

There is a strong demand for improvement of the retention force by whichthe abrasive is retained with respect to the tool cost, total workingcost, and surface roughness of a work material. To maintain thesharpness without increasing the value of the grinding power, it becomesnecessary to restore it by proper falling-off and crushing of abrasivegrains.

DISCLOSURE OF INVENTION

The present invention provides an abrasive which can attain a sufficientretention force in a resinoid grinding wheel even in the case of smallgrain size, a method of producing the same, and grinding wheel, coatedabrasives which use the same.

The present inventors have intensively researched to achieve the aboveobjects. As a result, they have found a method which can yield asufficient retention force on an abrasive in a resinoid grinding wheeleven in the case of a small grain size and also can suppress an increasein value of grinding power, and thus the present invention has beencompleted. The present invention is directed to the following:

-   -   (1) A metal-coated abrasive comprising a metal and plural        abrasive grains bonded by the metal;    -   (2) The metal-coated abrasive according to (1), wherein the        abrasive grains are coated with a metal layer;    -   (3) The metal-coated abrasive according to (2), wherein the        metal layer, with which the abrasive grains are coated, is        formed of plural layers;    -   (4) The metal-coated abrasive according to (2) or (3), wherein        the metal layer, with which the abrasive grains are coated,        contains at least one metal selected from the group consisting        of nickel, nickel-phosphorus, cobalt, cobalt-phosphorus,        titanium, copper, chromium, iron, zirconium, niobium, molybdenum        and tantalum;    -   (5) The metal-coated abrasive according to (4), wherein the        metal layer, with which the abrasive grains are coated, contains        nickel or nickel-phosphorus;    -   (6) The metal-coated abrasive according to (4), wherein the        metal layer other than an outermost metal layer, with which the        abrasive grains are coated, contains cobalt or        cobalt-phosphorus;    -   (7) The metal-coated abrasive according to any one of (3) to        (6), wherein the outermost metal layer of the metal layer, with        which the abrasive grains are coated, is formed of either nickel        or nickel-phosphorus;    -   (8) The metal-coated abrasive according to (2), wherein the        metal layer, with which the abrasive grains are coated, is        formed of a single layer of nickel or nickel-phosphorus;    -   (9) The metal-coated abrasive according to any one of (1) to        (8), wherein the metal, by which the abrasive grains are bonded,        contains at least one metal selected from the group consisting        of nickel, nickel-phosphorus, cobalt and cobalt-phosphorus;    -   (10) The metal-coated abrasive according to (9), wherein the        metal, by which the abrasive grains are bonded, is nickel or        nickel-phosphorus;    -   (11) The metal-coated abrasive according to any one of (1) to        (10), wherein the abrasive grains have an average grain size of        0.5 to 300 μm;    -   (12) The metal-coated abrasive according to (11), wherein the        abrasive grains have an average grain size of 1 to 150 μm;    -   (13) The metal-coated abrasive according to any one of (1) to        (12), wherein the abrasive grains comprise at least one selected        from the group consisting of cubic boron nitride, diamond,        alumina and silicon carbide;    -   (14) The metal-coated abrasive according to (13), wherein the        abrasive grains comprise one of cubic boron nitride, diamond,        and a mixture thereof;    -   (15) The metal-coated abrasive according to any one of (1) to        (14), wherein average 2 to 100 abrasive grains are bonded by the        metal;    -   (16) The metal-coated abrasive according to (15), wherein        average 2 to 50 abrasive grains are bonded by the metal;    -   (17) A grinding wheel using a metal-coated abrasive containing        5% by weight or more of the metal-coated abrasive of any one        of (1) to (16);    -   (18) The grinding wheel according to (17), which is a resinoid        grinding wheel;    -   (19) Coated abrasives using the metal-coated abrasive of any one        of (1) to (16);    -   (20) A method of producing the metal-coated abrasive of any one        of (2) to (8), which comprises forming a metal layer, with which        abrasive grains are coated, using an electroplating or        electroless plating method;    -   (21) A method of producing the metal-coated abrasive of any one        of (1) to (16), which comprises bonding plural abrasive grains        by a metal using an electroplating or electroless plating        method; and    -   (22) A method of producing the metal-coated abrasive of any one        of (2) to (16), which comprises dipping abrasive grains in an        electroplating or electroless plating bath to form a metal layer        on the surface of the abrasive grains while stirring, and        bonding the abrasive grains coated with the metal layer while        gently stirring.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing an example of a metal-coated abrasiveof the present invention.

FIG. 2 is a schematic view showing another example of a metal-coatedabrasive of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The metal-coated abrasive of the present invention comprises a metal andplural abrasive grains bonded by the metal. In this case, each of theabrasive grains is preferably coated with a metal layer in advance toform a metal-coated abrative grain. Alternatively, plural abrasivegrains may be coated with a metal layer.

In FIG. 1 and FIG. 2, the metal-coated abrasive of the present inventionis schematically shown. As shown in FIG. 1, the metal-coated abrasive ofthe present invention has a structure such that each of abrasive grains1 is coated with a metal layer 2 and the metal-coated abrasive grainsare bonded by a metal 3. As shown in FIG. 2, the metal-coated abrasiveof the present invention may have a structure such that plural abrasivegrains 4 are coated with a metal layer 5 in the state of being bonded,and are bonded with other metal-coated abrasive grains 6 by a metal 7.In this case, the metal layer 2 and the bonding metal 3 may be made ofthe same or different kinds of metal. Also the metal layer 5 and thebonding metal 7 may be made of the same or different kinds of metal.

Since the metal-coated abrasive of the present invention has such astructure, the retention force in the resinoid bond is increased ascompared with a conventional single-grain metal-coated abrasive, andthus it is made possible to suppress falling-off of the abrasive duringgrinding and to remarkably improve the grinding ratio. This effect isremarkably exerted in the case of abrasive grains having a small grainsize.

Taking the case of cBN, a conventionally used metal-coated abrasive isan abrasive obtained by coating a single abrasive grain with a single-or multi-layered metal such as nickel, nickel-phosphorus, cobalt,cobalt-phosphorus or titanium and is produced so that the resultingabrasive does not contain plural abrasive grains bonded by metalcoating, like the metal-coated abrasive of the present invention.Therefore, as the grain size of abrasive grains decreases, smallirregularities are formed on the coated surface, and also the number ofirregularities on the surface is reduced. Therefore, the retention forcein the resinoid bond is reduced and the abrasive often falls off duringgrinding, resulting in low grinding ratio. In the case of themetal-coated abrasive of the present invention, since irregularitiesformed by bonding the metal-coated abrasive grains serve as an anchor inthe resinoid bond, the retention force of the metal-coated abrasive inthe resinoid bond is improved, and the grinding ratio is improved.

The resinoid grinding wheel using the metal-coated abrasive of thepresent invention exhibited lower value of the grinding power ascompared with a conventional abrasive (composite abrasive grains)obtained by bonding plural abrasive grains using a vitrified-bondmaterial or a metal bond material, and also exhibited the same value ofthe grinding power as that of a conventional resinoid grinding wheelusing a single-grain metal-coated abrasive.

The reason is considered as follows. Although the metal-coated abrasiveof the present invention exhibits the same retention force by which theabrasive is retained in the resinoid bond as that of a conventionalabrasive (composite abrasive grains) obtained by bonding plural abrasivegrains using a vitrified-bond material or a metal bond material, theabrasive grains are bonded by a metal having a smaller bonding forcethan that of the vitrified-bond material or metal bond material, andthus the abrasive grains fall off from the bonding metal portion when alarge load is applied and then produce new abrasive grains which serveas a cutting edge, thereby preventing an increase in value of thegrinding power.

The abrasive grains used in the present invention may be made of eithersingle crystal or polycrystal and also may be subjected to any surfacetreatment. As shown in FIG. 2, plural abrasive grains may be bondedtogether by sintering or other methods.

The average grain size of the abrasive grains used in the metal-coatedabrasive of the present invention is preferably within a range from 300to 0.5 μm, and more preferably from 150 to 1 μm. When the average grainsize exceeds 300 μm, bonding of the abrasive grains tends to exert asmall effect. On the other hand, when the average grain size is lessthan 0.5 μm, it becomes difficult to control the degree of bonding ofthe abrasive grains in the case of providing the surface of the abrasivegrains with a metal coating.

The number of the abrasive grains to be bonded together in themetal-coated abrasive of the present invention is preferably within arange from 2 to 100, and more preferably from 2 to 50. When more than100 abrasive grains are bonded together, the resulting metal-coatedabrasive tends to be too large and distribution of the metal-coatedabrasives in the resinoid grinding wheel tends to become non-uniform,and thus the quantity of abrasion at the abrasive-free portion tends toincrease during grinding and the grinding ratio tends to be lowered.

The metal layer coating the abrasive grains preferably contains at leastone metal selected from the group consisting of nickel,nickel-phosphorus, cobalt, cobalt-phosphorus, titanium, copper,chromium, iron, zirconium, niobium, molybdenum and tantalum. In the casein which the metal layer is composed of a single layer, it is preferablyformed of nickel or nickel-phosphorus. In the case in which the metallayer is composed of two or more layers, an outermost metal layer ispreferably formed of nickel or nickel-phosphorus. In the case in whichthe metal-coated abrasive grains are not completely coated with themetal layer, with which the abrasive grains are bonded, an outermostmetal layer is preferably formed of nickel or nickel-phosphorus. Becausenickel and nickel-phosphorus have good corrosion resistance, they arepreferably selected for forming the outermost metal layer. In the casein which plural metal layers are formed, inner metal layers (layersother than the outermost metal layer) are preferably formed of cobalt orcobalt-phosphorus. Since cobalt and cobalt-phosphorus have largeresistance to deformation at high temperature and suppress deteriorationdue to grinding heat, they can protect the abrasive grains by preventingthe abrasive grains from falling off and achieve the effect of improvingthe grinding ratio.

In the metal-coated abrasive of the present invention, the metal, bywhich the metal-coated abrasive grains are bonded together, preferablycontains at least one kind selected from the group consisting of nickel,nickel-phosphorus, cobalt, and cobalt-phosphorus. Among these metals,nickel or nickel-phosphorus is preferably used in view of corrosionresistance and productivity. The metal may be the same kind as that usedin the metal layer.

Examples of the abrasive grains used in the metal-coated abrasive of thepresent invention include cubic boron nitride, diamond, alumina, siliconcarbide, and other powdered hard substances. These hard substances maybe used alone or in combination. When using cubic boron nitride,diamond, or a mixture thereof as abrasive grains, particularlyremarkable effects can be obtained. Since cubic boron nitride anddiamond are excellent in abrasive grain strength but have relativelyinsufficient retention force by which the abrasive grains are retainedin the bond, the effect obtained by the metal coating of the presentinvention is larger than that of the other hard substances and aremarkable effect can be obtained.

In the formation of the metal layer of the metal-coated abrasive grainof the present invention, known methods such as electroplating andelectroless (chemical) plating methods can be used. Among these methods,an plating method is preferably used.

The method of coating the metal layer on the abrasive grains accordingto the present invention will now be described using the case wherenickel coating (nickel-phosphorus coating) is conducted by anelectroless (chemical) plating method.

Before the nickel coating conducted by an electroless plating method, ametal (for example, palladium) serving as a nucleus for deposition ofnickel is preferably deposited on the surface of the abrasive grains.For example, the method of depositing a palladium metal (activationtreatment) after dispersing and applying tin chloride on the surface ofthe abrasive grains (sensitization treatment) is commonly used, and canbe conducted in a known manner.

Then, the abrasive grains are subjected to electroless plating whereinnickel is deposited on the surface of the abrasive grains by dipping inan electroless plating bath (for example, a mixed bath of nickelsulfate, sodium hypophosphite, sodium acetate, sodium citrate andsulfuric acid). In this case, the electroless plating bath is mixed withvigorous stirring so that the abrasive grains are not bonded by a metalto be plated. Since this state varies depending on the size and shape ofthe plating bath and the size and shape of the stirring blade,conditions must be set for each apparatus.

In the stage where a nickel coating is formed on the surface of abrasivegrains, stirring is performed slowly by reducing the revolution rate ofthe stirring blade, and thereby the abrasive grains are bonded. In thatcase, the degree of bonding is controlled by the rate at which stirringis slowed and the retention time.

After the completion of metal coating, the metal-coated abrasive istaken out from the plating bath, washed with water, dried and thenshifted through a sieve to obtain a metal-coated abrasive having apredetermined size of the present invention.

A grinding wheel of the present invention contains the metal-coatedabrasive. The content of the metal-coated abrasive of the presentinvention in the grinding wheel is preferably 5% by weight or more, andmore preferably 25% by weight or more. When the content of themetal-coated abrasive is less than 5% by weight, sufficient effect ofthe use of the metal-coated abrasive of the present invention is notexerted and the grinding ratio is hardly improved.

In the case in which the resinoid grinding wheel is produced by usingthe metal-coated abrasive of the present invention, a higher grindingratio is obtained as compared with the case of using a conventionalsingle-grain metal-coated abrasive, and thus grinding cost is reduced.In the case of the resinoid grinding wheel using the metal-coatedabrasive comprising abrasive grains having a very small grain size, aremarkable effect is exerted. In that case, the value of the grindingpower is the same as in the case of using a conventional single-grainmetal-coated abrasive. The surface roughness of the work material aftergrinding is improved as compared with the case of using a conventionalsingle-grain metal-coated abrasive.

As the bond of the resinoid grinding wheel of the present invention, acommercially available resinoid bond can be used according to theapplication field. Examples of the bond include bonds made mainly of aphenolic polymer compound and a polyimide-type polymer compound. Theamount of the bond in the grinding wheel is preferably controlled withina range from 25% to 90% by volume. When the amount of the bond is lessthan 25% by volume, the retention force by which the abrasive isretained is reduced and, as a result, the abrasive often falls off asthe grinding ratio is reduced. On the other hand, when the amount of thebond is more than 90% by volume, the amount of the abrasive grains isreduced and, therefore, the resulting abrasive is not suitable for usein a grinding tool.

In the resinoid grinding wheel of the present invention, there can alsobe used additives, which are commonly used in the production of theresinoid grinding wheels, such as solid antifriction agents, auxiliarybonding materials, aggregates, and/or porous materials.

EXAMPLES

The following Examples illustrate the present invention in detail, butare not intended to limit the present invention.

Example 1

1 kg of cBN abrasive grains SBN-B, manufactured by SHOWA DENKO K.K.(nominal grain size: G-30, average grain size: 22 μm) was subjected to asensitization treatment and an activation treatment. Specifically, theabrasive grains were dipped in 1 liter of an aqueous tin chloridesolution prepared by adding distilled water to 1 g of tin chloride and10 ml of hydrochloric acid, subjected to the sensitization treatmentwhile maintaining with stirring at room temperature for 2 minutes, takenout from the aqueous solution, and then slightly washed with water.Thereafter, the abrasive grains were dipped in 1 liter of an aqueouspalladium chloride solution prepared by adding distilled water to 0.5 gof palladium chloride and 75 ml of hydrochloric acid, subjected to theactivation treatment while maintaining with stirring at room temperaturefor 2 minutes, taken out from the aqueous solution and then slightlywashed with water.

The abrasive grains subjected to the sensitization treatment and theactivation treatment were dipped in 25 liters of a plating bath preparedaccording to the formulation shown in Table 1. After adjusting the pH to5 using sulfuric acid, the plating bath was heated to 90° C. and stirredat 60 rpm using a stirrer. For the plating bath, an aqueous sodiumhypophosphite solution (5 mol/liter) was used until the plating bathbecame transparent, and then the abrasive grains were subjected tonickel coating (nickel-phosphorus coating) using an electroless platingmethod.

After the plating bath became transparent, the revolution rate of thestirrer was decreased to 45 rpm and 25 liters of a plating bath (the pHwas adjusted to 5 using sulfuric acid and was heated to 90° C.) preparedaccording to the formulation shown in Table 1 was additionally chargedin order to bond the nickel-coated abrasive grains. In the plating bath,an aqueous sodium hypophosphite solution (5 mol/liter) was added untilthe plating bath became transparent, and then nickel coating wasconducted using an electroless plating method.

After the plating bath became transparent, the coated abrasive grains(metal-coated abrasive) were taken out from the plating bath, washedwith water, dried and sifted through a sieve having an opening size of50 μm, and then a metal-coated abrasive on the sieve was collected. SEMresults revealed that metal-coated abrasive comprising about 2 to 10abrasive grains accounts for 100%.

A portion of the metal-coated abrasive was taken out and the metalcoating was dissolved using an acid, and then a weight ratio of themetal layer was calculated. As a result, it was 60.4% by weight.

Comparative Example 1

Under the same conditions as in Example 1, 1 kg of cBN abrasive grainsSBN-B, manufactured by SHOWA DENKO K.K. (nominal grain size: G-30,average grain size: 22 μm) were subjected to a sensitization treatmentand an activation treatment, and were then dipped in 50 liters of aplating bath prepared according to the formulation shown in Table 1.After adjusting the pH to 5 using sulfuric acid, the plating bath washeated to 90° C. and stirred at 60 rpm using a stirrer. In the platingbath, an aqueous sodium hypophosphite solution (5 mol/liter) was addeduntil the plating bath became transparent, thereby the abrasive grainswere subjected to nickel coating (nickel-phosphorus coating) using anelectroless plating method.

After the plating bath became transparent, the metal-coated abrasive wastaken out from the plating bath, was washed with water, was dried, andthen was collected. SEM results revealed that metal-coated abrasivecomprising about 2 or more abrasive grains bonded to each other were notpresent.

A portion of the metal-coated abrasive was taken out and the metalcoating was dissolved using an acid, and then a weight ratio of themetal layer was calculated. As a result, it was 60.4% by weight.

Comparative Example 2

Based on the descriptions of Japanese Patent Application, FirstPublication No. Hei 10-337670, composite abrasive grains were produced.cBN abrasive grains SBN-B, manufactured by SHOWA DENKO K.K. (nominalgrain size: G-30, average grain size: 22 μm) and a borosilicate-basedvitrified bond (grain size: 5 μm or less) which accounts for 30% byweight of SBN-B were charged in a stirring type granulator, and then astirring blade was rotated at 500 rpm and a pulverizing blade wasrotated at 2000 rpm. Granulation was conducted by spraying a binder (5wt % cellulose/ethanol) over powders obtained by sufficiently mixingSBN-B with the vitrified bond and passing through a pulverizing bladeportion. After drying and sifting through a sieve having an opening sizeof 20 μm, abrasive grains on the sieve were collected.

The surface of the collected abrasive grains was partially coated with avitrified bond. A portion of the abrasive grains was taken out and thebinder was dissolved in an alcohol by ultrasonic cleaning and a weightratio of the coating (vitrified bond and binder) was calculated. As aresult, it was 20% by weight.

100 g of the collected abrasive grains were mixed with 1 kg of SBN-B(nominal grain size: G-30, average grain size: 22 μm) and the mixturewas subjected to a heat treatment in an atmospheric air at 900° C. forone hour, thereby to dissolve the vitrified bond, with which the surfaceof the collected abrasive grains is coated, and to bond the abrasivegrains, and thus composite abrasive grains were obtained. After coolingto room temperature and sifting through a sieve having an opening sizeof 50 μm, composite abrasive grains on the sieve were collected. SEMresults revealed that composite abrasive grains comprising about 2 to 10abrasive grains bonded with each other accounted for approximately 100%.

Example 2 and Comparative Examples 3 and 4

Using the abrasive grains produced in Example 1 and Comparative Examples1 and 2, resinoid grinding wheels were produced.

The shape and formulation of the resulting grinding wheels are shownbelow. The shape of the grinding wheel is represented by the symboldefined in JIS B 4131 (diamond and cubic boron nitride wheel), while thesymbol 1A1 denotes the shape of the grinding wheel and symbols D, U, Xand H respectively denote outer diameter of the grinding wheel, width ofthe grinding wheel (abrasive grains layer), thickness of abrasive grainlayer, and hole diameter of the attaching portion (unit: mm).

Shape of grinding wheel:

-   -   1A1 shape: 150D×5U×3X×76.2H

Formulation:

-   -   Abrasives: 30.6% by volume    -   Resinoid bond: 69.4% by volume (phenol resin)

Example 3 and Comparative Examples 5 and 6

With respect to resinoid grinding wheels obtained in Example 2 andComparative Examples 3 and 4, a grinding test was conducted under thefollowing conditions. The results of the grinding test are shown inTable 2.

Grinding machine: horizontal spindle surface grinding machine

-   -   (axial motor of grinding wheel: 3.7 kW)    -   Work material: SKH-51 (HRc=62 to 64)    -   Surface of work material: 200 mm×100 mm    -   Grinding system: wet surface traverse grinding system Grinding        conditions:        -   Peripheral speed of grinding wheel: 1500 m/min        -   Table speed: 15 m/min.        -   Cross feed: 2 mm/pass        -   Depth of cut: 2 μm

Grinding fluid: JIS W2 soluble type, exclusive fluid for cBN TABLE 1Formulation of nickel plating bath Water 50 liter Nickel sulfate 25 molSodium acetate 75 mol Sodium citrate 10 mol

TABLE 2 Results of grinding test Value of Surface Grinding grindingroughness ratio power (W) Ra (μm) Example 3 523 225 0.05 Comparative 305230 0.09 Example 5 Comparative 481 355 0.07 Example 6

Industrial Applicability

Since the metal-coated abrasive including a metal and plural abrasivegrains bonded by the metal has a higher retention force by which theabrasive is retained in a resinoid bond than that of a conventionalmetal-coated abrasive, falling-off of the abrasive is reduced, andtherefore it becomes possible to produce a resinoid grinding wheel,coated abrasives, which can achieve a higher grinding ratio. In thatcase, a value of the grinding power is the same as that in the case ofusing a conventional single-grain metal-coated abrasive and the surfaceroughness of a work material is improved.

1. A metal-coated abrasive comprising a metal and plural abrasive grainsbonded by the metal.
 2. The metal-coated abrasive according to claim 1,wherein the abrasive grains are coated with a metal layer.
 3. Themetal-coated abrasive according to claim 2, wherein the metal layer,with which the abrasive grains are coated, is formed of plural layers.4. The metal-coated abrasive according to claim 2 or 3, wherein themetal layer, with which the abrasive grains are coated, contains atleast one metal selected from the group consisting of nickel,nickel-phosphorus, cobalt, cobalt-phosphorus, titanium, copper,chromium, iron, zirconium, niobium, molybdenum, and tantalum.
 5. Themetal-coated abrasive according to claim 4, wherein the metal layer,with which the abrasive grains are coated, contains nickel ornickel-phosphorus.
 6. The metal-coated abrasive according to claim 4,wherein the metal layer other than an outermost metal layer, with whichthe abrasive grains are coated, contains cobalt or cobalt-phosphorus. 7.The metal-coated abrasive according to any one of claims 3 to 6, whereinthe outermost metal layer of the metal layer, with which the abrasivegrains are coated, is formed of either nickel or nickel-phosphorus. 8.The metal-coated abrasive according to claim 2, wherein the metal layer,with which the abrasive grains are coated, is formed of a single layerof nickel or nickel-phosphorus.
 9. The metal-coated abrasive accordingto any one of claims 1 to 8, wherein the metal, by which the abrasivegrains are bonded, contains at least one metal selected from the groupconsisting of nickel, nickel-phosphorus, cobalt and cobalt-phosphorus.10. The metal-coated abrasive according to claim 9, wherein the metal,by which the abrasive grains are bonded, is nickel or nickel-phosphorus.11. The metal-coated abrasive according to any one of claims 1 to 10,wherein the abrasive grains have an average grain size of 0.5 to 300 μm.12. The metal-coated abrasive according to claim 11, wherein theabrasive grains have an average grain size of 1 to 150 μm.
 13. Themetal-coated abrasive according to any one of claims 1 to 12, whereinthe abrasive grains comprise at least one selected from the groupconsisting of cubic boron nitride, diamond, alumina and silicon carbide.14. The metal-coated abrasive according to claim 13, wherein theabrasive grains comprise one of cubic boron nitride, diamond, and amixture thereof.
 15. The metal-coated abrasive according to any one ofclaims 1 to 14, wherein average 2 to 100 abrasive grains are bonded bythe metal.
 16. The metal-coated abrasive according to claim 15, whereinaverage 2 to 50 abrasive grains are bonded by the metal.
 17. A grindingwheel using a metal-coated abrasive containing 5% by weight or more ofthe metal-coated abrasive of any one of claims 1 to
 16. 18. The grindingwheel according to claim 17, which is a resinoid grinding wheel. 19.Coated abrasives using the metal-coated abrasive of any one of claims 1to
 16. 20. A method of producing the metal-coated abrasive of any one ofclaims 2 to 8, which comprises forming a metal layer, with whichabrasive grains are coated, using an electroplating or electrolessplating method.
 21. A method of producing the metal-coated abrasive ofany one of claims. 1 to 16, which comprises bonding plural abrasivegrains by a metal using an electroplating or electroless plating method.22. A method of producing the metal-coated abrasive of any one of claims2 to 16, which comprises dipping abrasive grains in an electroplating orelectroless plating bath to form a metal layer on the surface of theabrasive grains while stirring, and bonding the abrasive grains coatedwith the metal layer while gently stirring.